Female seed beetles, Callosobruchus maculatus, remate for male-supplied water rather than ejaculate nutrition

Abstract

Female seed beetles, Callosobruchus maculatus, mate multiply even though association with males and copulations carry costs, such as injury to the genital tract. Multiple mating (polyandry) may, however, offset these costs through the acquisition of food and water, two material benefits hypothesized to be obtained from the large ejaculates produced by males. The material benefits hypothesis can be tested by increasing female access to nutrients and water, with the prediction that female mating frequency will decrease as copulation is no longer required to derive these materials. Females were given water, 5% sugar-water or baker's yeast, and were compared with females deprived of these. We presented females with virgin males daily for 8 days and recorded female mating frequency, survivorship, and fecundity. Females provided with water and sugar-water decreased mating frequency. Thus, water, rather than nutrients in the ejaculate, appears to be important to females of this species. In addition, both life span and fecundity were extended for females in the sugar-water and water treatments. Since water is scarce in the arid environment in which this species is found, we conclude that polyandry provides material benefits to females that may offset some of the costs of associating with males.